Range finder



July 9; 1946.

S. M. MacNEILLE 2,403,732 f RA'NGE FINDER Filed March 11, I944 HGJ. 1 V

STEPHEN M.MACNEILLE v 64 INVENTOR I WMW ATTY & AGT

July 9, 1946. i s. M. MacNElLL E RANGE FINDER Filed March 11', 1944 s Shets-Sheet 2 FIG.5.

FIG.4.

STEPHENMJMCNEILLE INVENTOR BY my ATTY AG'T July 9, 1946. s. M. MaQN EILLE RANGE FINDER FiledMarch 11, 1944 3 Sheets-Sheet 3 FIG. 10.

v .T G M M m M W m W m m m, w S s: c: h :2 cc 3 .cidence within a wide range.

Patented July 9, 1946 UNITED STATES PATENT OFFICE I RANGE FINDER 7 Stephen M. MacNeille, Oak Ridge, Tenn, assignor to Eastman Kodak Company, Rochester,

N. 11, a corporation of New Jersey Application March 11, 1944, Serial No. 526,020 (c1. 88- -2.'7)

12 Claims.

This invention relates to range finders. This applicationis a continuation in part of one entitled Range finders, 'case P, Serial No. 505,016, filed October 5, 1943, and in the series it replaces that application and becomes case P.

The object of the present invention is to provide an accurate range finder of the invert splitfleld type primarily for an ortho-pseudo-stereo finder but also usefulin those of the coincidence type.

Most ortho-pseudo-stereo range finders in the past have had independent means for forming the right and left eye fields, or as in-case K, Serial No. 479,101, filed March 13, 1943, Mihalyi and MacNeille, have had two fields with a relay lens system to image each field adjacent to the other. It is an object of thepresent invention to provide a system for producing both the right and left eye fields in a single plane. It is a primary object to do this in a symmetrical manner,

thereby eliminating many of the errors which I posite directions.

beam splitter described in my copending a-pplication is the preferred one because of the possibility of selecting any desired angle of in- It consists of alternate layers of materials of high and low indices of refraction with thicknesses approximating that efiectively equal to one quarter of the wave length of light so that by optical interference, the composite multilayer material selectively reflects and transmits light of opposite polarizations.

According to the present invention the range finder is made up with two viewing points and some means such as pentaprisms for directing the light beams, received from the target being ranged, directly toward each other along an optical axis. To one side of this axis and coplanar therewith, there is located a semi-transparent, semi-reflecting mirror to act as a beam combiner. In line with each beam are two reflectors such as prisms oriented to reflect the beams to the combining reflector from opposite sides and to rotate the beams through 90 in op- 2 If, due to the presence of suitable objectives, an image is formed at or near the combining reflector, it. is obvious that the rotation of the beams gives the required invert field effect. However, the effect is the same whereever the images are formed and the prism unit used can actually be anywhere in the beams with respect to these images; in fact, the light may be I colllmated as it travels through the prism unit.

One embodiment of the invention has the prism in the converging beam optically following a pair of relay lenses which form images in the focal planes of the eyepieces. This embodiment re quires the field separating means to be located at the primary images, i. e. to have the primary images opaque over one-half of their total area and requires the dividing line'to be carefully adjusted. A second embodiment has the images formed at or near a beam combiner, with an additional set of relay lenses for relaying these images tothe eye pieces. Since the images are in the same prismunit and since the opaquing of half of each field'is accordingly provided by masks on this prism unit, the dividing line can be carefully adjusted once and for all when the prism assembly is made and will remain accurate probably for the whole life of the instrument.

If the finder is to be used as a coincidence type,

the pair. of images are viewed from one side of the combining reflector, whereas if the instrument is to be used as a stereo range finder, means are provided for viewing both beams from one side of the reflector with one eye and both beams from the other side of the reflector with the other eye. Preferably, a similar pair of reflectors is included optically to follow the beamcombining reflector, to receive the light from i/% sin% sin is quite satisfactory. For convenience and to permit the eXit system to be symmetrical with the entrance system, I preferably arranged the angle between the incident beam and the combining reflector to be 45. In this case the dihedral angle between each pair of reflecting surfaces in the entrance system should be 6219, 7858, 101D2 or 11731'.v In the most preferred form of the invention I arrange the prisms so that the angle of incidence at each of the two reflections are equal. In this case the prisms which constitute the refleeting surfaces can all be made identical to each other, although their shape is somewhat unusual when they are out to be, as compact as possible for any given aperture.

The prism unit for combining these light beams is useful in any system where two beams approach each other and are to be combined symmetrically.

The invention will be fully understood from the following description of the preferred embodiment thereof when read in connection with the accompanying drawings, in which Fig. 1 is a plan view of an optical system for an ortho-pseudo-stereo range finder incorporating a simple embodiment of the invention, Figs. 1A and 1B showing the fields in the primary image planes thereof.

Fig. 2 shows a binocular field of view through the instrument shown in Fig. 1.

Fig. 3 shows diagrammatically an end View of the prism unit shown in Fig. 1.

Figs. 4 and 5 are perspective views shaded to show the structure of the prism unit and corresponding respectively to the views shown in Figs. 1 and 3.

Figs. 6A to 6F are various views of the individual prism units, eight of which are combined with the simple unit shown in Fig. 7 to form the total unit shown in Figs. 4 or 5.

Fig. 7 shows a prism unit in the cemented surface of which is included a semi-transparent, beam-combining reflector.

Figs. 8 and 9 show an alternative embodiment using simple mirrors in place of prisms and illustrating the rotation of the beams.

Fig. 10 is similar to Fig. 1 and illustrates a'preferred embodiment of the invention.

Fig. 11 is similar to Fig. 5 but corresponds to the embodiment shown in Fig. 10.

Fig. 12 is a perspective view corresponding to Figs. 4 and 5 (or to Fig. 11).

In Fig. 1 light from a target being ranged is received at spaced viewing points, by optical squares l and directed through objectives ll into focus in right and. left fields l2 and 13 respectively, adjacent to which are located fleld lenses. The deviation of one beam relative to the other is provided in the usual way by a light deviator I4. It will be noted that the two beams are directed exactly toward each other along optical axis l and are not offset in any way. Figs. 1A and 1B show the two fields l2 and 13 with images 20 and 2! of the target respectively in each field. The lower half of each field is masked off so that when the two fields are brought together in in: verted relation, there will be nooverlapping of the images. Relay lenses 22 and 23 are employed to re-image the light beams in the focal plane of the eyepieces, but various other optical systems may be used for this purpose including double relay systems. By means of prism units 25 and 26, light from the right and left viewing point image planes is directed respectively to opposite sides of a beam-combining reflector 24 which is located co-planar with the axis 55 and to one side thereof. The path of the light is perhaps bestseen in Fig. 3. As the beams strike the beam-combining reflector 24 they are both in a plane which is orthogonal to the axis I5 and, in this plane, they strike the reflector 24 at an angle A. Each beam is split by the combining reflector 24 so that through prism 21 parts of each beam pass to the right eye and through prism 28 parts of each beam pass to the left eye. Additional prisms 3Z8, rhombs 3i and eyepleces 32 have been provided to permit stereo viewing of these images.

The actual fields of views 35 and 3% are shown in Fig. 2. The image 28 from the primary plane i2 is split by the semi-reflector 24, so that the right eye sees the image 20 by reflection and the left eye sees it (marked 29' in Fig. 2) by transmission. Similarly, the left eye sees the image 21 by reflection and the right eye sees it (marked M) by transmission. In the prism unit 25 the light from the image I2 is reflected twice before it strikes the beam-combiner 24, the two reflecting surfaces being oriented to rotate the beam through 90. From the symmetry of the arrangement, it will be seen that the beams are rotated in opposite directions so that the images are inverted one with respect to the other and do not overlap because of the masking of the lower half'of each of the primary image planes.

In addition to all of the advantages of orthopseudo-stereo range finders combined with the advantages of invert field range finders, the present system has the advantage of symmetry, namely, constancy of image size, uniformity of illumination and balancing out of various errors and aberrations. Each eye sees an invert field which may be separately used for simple coincidence type of ranging.

In Figs. 1 to 3, the actual angleA is not specifled and the reflections in the prism units may be at different angles of incidence. However, if for the sake of symmetry, one further specifies that the angles of incidence at each reflection be equal, and the angle A be then the simplest form of prism unit which can be made up from eight identical prisms and a pair of right angle prisms having the beam combiner cemented and hypotenuse surfaces is shown in Figs. 4-7. Light from the left viewing point is reflected by prisms 4t and 4! through prism M to the beam-combining reflector 24 and similarly light from the right viewing point is reflected by prisms 42 and 43 through prism 45 to the other side of the beamcombiner 24. An identical exit system is made up of prisms lt, 4?, 48 and 49. The details are shown in Figs. 6 and 7. Each prism unit is essentially a simple one with entrance and exit faces 50 and 52 and a single internal reflecting surface 5!. To permit assembly of the prisms in the minimum space, corners of each prism not used for transmitting light are cut away. Furthermore, to permit the eight reflecting prisms to be identical, certain additional facets are cut unnecessarily on the outer prisms 4i and 32, say, but which correspond to necessary facets on prisms 4i and 43 to permit assembly; Similarly, certain facets which are necessary .on the outer prisms appear on the inner .prisms'but are unnecessary here.

image's-'80 and T traveling toward eachother' along axis strike mirrors '81 and 'H,-respe'c- 'tively, the orientation of the beams at this surface being shown by arrows 62 and I2. 1 The reflected beams then strike mirrors-83 and I3 respectively, the orientation being shown by arrows 64 and I4 and travel thence to the beamcombining reflector 24 to strike opposite sides thereof-with the beams 65 and 15 inverted relative to one another. of the images 60 and I0 is masked off as in Fig. 1, the resulting beams at the beam-combiner-24, or wherever the actual images are formed, are of the split-field invert-type. I

In a preferred embodiment of the invention, the beam-combiner 24 is made ofan optical interference multilayer film to reflect and transmit light of opposite polarization. The focal planes I2 and I3 may then be optically after the prism unit and separation of the field is then provided by two polarizing filters, respectively, over each half of each field with their vibration axes mutually at right angles. It will be noted that no polarizing filter or other selecting filter is necessary in embodiments of the invention wherein the If the lower half of each bly in the form of a biconcave or plane-concave.

airspace if this is desired. In any case the lenses 82,- 83 and 85 should be of suflicient diameter toutilize substantially 'all'of the entrant and exit facesof the prism assembly,

In' Fig. 10 the whole lens system considered as one for forming the image near the beamcombining reflector. Thatis, the primary images themselves may be formed inthe .prism-84 bya single lens in place of the lenses 'll,80'and82.

' When the beam combining refle'ctoris of the polarizing type, the adjacent'image plane may be in the position shown with masks 81 and 88 for cutting off complementary halves or alternatively may be anywhere in the unit includingplanes optically following the beam combining reflector. For example if the images are formed on the exit faces of the prisms 84 instead of on the entrant faces, the masks 8'l and focal planes I2 and 13 are ahead of the prism unit and are masked over half of their field.

In Fig. 10 the primary images are formed on field lenses 8!] and 8| which differ from Fig. 1 by the fact that there is no opaque mask covering half of the images at these points. These images are relayed by lenses 82 and 83, which are of shorter focal length thanthe corresponding lenses of Fig. 1, so that in the presentcase the images are formed on the optical front surfaces of prisms 84 (corresponding to 44 and 45 of Fig. 5). These images are then relayed by additional relay lenses 85 to form images in the focal planes of the eyepiece 32. To permit the lenses 85 to be located; in the positions shown longer rhombs 19 are used to replace. the rhombs 3| in Fig. 1. At these secondary images on the surfaces of the prisms 84, masks 81 and 88 are located opaqing one-half of each image (see Fig. 11). This is indicated by the stoppage of the light represented by arrows 9| and 92, whereas the light represented by arrows 93 and 94 passes through in each case to be split at the semi-transparent mirror surface. The position of the mask 81 is unique, but except for the slight out of focus edge,.the mask 88 could be replaced by one located by positions shown by broken line 96. A mask in the position 88 is preferable however. The edges 89 and 90 of the masks must correspond optically to one another since they. represent and produce the dividing line in the ultimate field. This is one of the chief advantages of this embodiment of the invention since the edges 89 and 9ll will stay in adjustment, once they are fixed whereas in Fig. l, the masks producing the dividing line are located on elements. I2. and I3 separated from each other so that they are liable to get out of adjustment. The advantages of having a clean, accurate dividing line without any overlapping and without any separation, is well known to any one who has used a split field range finder.

The double relay system in this embodiment shown in Fig. 10 has the additional advantage of optical efiiciency. If desireda field lens could be included near the center of the prism assem- 88 should be omitted. The complementary masking is then done by polarizing filters over the exit faces as'shown'by broken lines. I These broken-lines are drawn partly with long sectionsand partly with short sections= to represent schematically the orientation of the vibration: axis of the filters. The sections labelled 108 will serve to illustrate the function of the polarizing filter in this embodiment; Primarily-the polarizing filters must have exaetly'the same action as the opaque masks 81 and 88. That is the ray 94 must be transmitted by the filter I00, both the part reflected and the part transmitted at the beam combirling reflector 86. The part reflected at the surface 86 due to the polarizing action of this surface has its vibration'axis perpendicular to the plane of the paper and is hence transmitted by the filter I00. Similarly the part of the ray 94 which is transmitted by the plane of the paper and accordingly is trans mitted by the filter I00 as shown. Onjthe other hand the ray 9| which in this embodiment is not masked by any mask 88 is divided or split by the-"surface 86 but is-polarized therebyso that both the transmittedportionand the reflected portion are stopped by the polarizing filters 100. The other two parts of the polarizing filters are similarly arranged as shown to transmit both parts of the ray 93 but to stop bothparts of the ray 92. Obviously such an arrangement of polarizing filters can be used at the image planes wherever they are located, providing of course that the operation of the polarizing beam splitter is not adversely affected. 1

Fig. 12 is added merely for clarity in demonstrating the path of the two beams through the prism. As shown the two beams are combined and emerge only toward one eyepiece, the other emerging beam being omitted from the drawing since it would tend to confuse the picture. This Fig. 12 corresponds either to Figs. 4 and 5or to Fig. 11.

between the. viewing points [0 and the prism unit can be and to one side thereof, a pair of reflecting surfacesin each beam oriented to direct the beams to opposite sides of said reflector and to rotate thenrthrough 90 "in opposite directions, lens means for focusing each beamto form images which, due to the rotation of the beams, are inverted relative to one another and means for viewing the images from at least one side of the combining reflector.

,3. A range finder according to claim 1 in which the viewing means is binocular with right and left eye eyepieces for receiving respectively light from opposite sides of the combining reflector whereby ortho-pseudo-stereo fields are.

presented.

4. A range finder according to claim 2 including a similar pair of reflecting surfaces in each of the beams from opposite sides of the combining reflector.

5. A. prism unit for combining light beams which are approaching each other along an axis comprising a beam-combining reflector coplanar with the axis and to one side thereof, two entrance faces on the unit orthogonal to the axis and in line therewith to receive the beams, and reflecting surfaces on the unit for totally internallyreflecting each beam twice, oriented to. direct the beams to opposite sides of the combining reflector and to rotate the beams through 90? in opposite directions.

6. A prism unit including the combining unit according to claim 5 and an identical unit fol-'- relay system for relaying both images to each eyepiece, said relay, system including a beamcombining. reflector lyingcoplanar with said optical-axis and to one side thereof, a pair of refleeting surfaces in each beam oriented to direct the beams to opposite sides of said reflector and to rotate them through 90 in opposite-directions and relaylens means in each beam, corresponding halves of each of the primary image planes being masked off.

.8. .A range .finder comprising means at spaced viewing points-for receiving light beams from the target being ranged and for directing them toward each other along an optical axis, a beamcombining reflector for transmitting and reflect- 8 ing light of opposite polarizations lying coplanar with the axis and to one sidethereof, a pair of reflecting surfaces in each target beam oriented to direct the beams to opposite sides of said re- 1 flector and to rotate them through in opposite directions, lens means for. forming right and left viewing point images superimposed in inverted relation in right and left eye image planes optically after the said beam-combining reflector, a pair of polarizing filters with their vibration axis mutually at right anglesat and dividing each of the said image planes and means for stereoviewing the images.

9. A range finder comprising means at spaced viewing points for receiving light beams from the target being ranged and for directing them toward each other along an optical axis, an objective in each beam for forming images in primary image planes, right and left eye eyepieces and a relay system for relaying both images to. each eyepiece," said relay system including a beamcombining reflector lying coplanar with said optical axis and to one side thereof, a pair of reflecting surfaces in each beam oriented to direct the beams to opposite sides of said reflector and to rotate them through 90 in opposite directions, a relay lens in each beam for relaying the primary image to form a secondary image near the reflector, masking means at each of thesecondary image planes for masking ofi complementary halves of the images and secondary relay lens means for relaying the transmitted parts of both secondary images to each eyepiece.

10. A range finder according 'to claim 9 in which the secondary images are optically ahead of the beam-combining reflector and the masking means are opaque over one-half of each image.

11. A range finder according to claim 9 in which the beam combining reflector is'a polariz- 111g beam splitter for transmitting and reflecting light of opposite polarizations, the secondary images are formed optically after the reflector and the masking means at each image plane consists of a polarizing filter with adjacent halves oriented with their vibration axis at right angles to selectively mask the two images.

12. A range finder comprising means at spaced viewing points for receiving light beams-from the target being ranged and for directing'them toward each other along an optical axis, right and left eye eyepieces and means for directing both beams to each eyepiece including a beam combining reflector lying coplanar with said optical axis and to one side thereof, a pair of reflecting surfaces in each beam oriented to direct the beams to opposite sides of said reflector and to rotate them through 90 in opposite directions, lens means in each beam optically between the viewing point and the reflecting surfaces for forming near the beam combining reflector an image of the target, the two images being optically inverted relative to one another, masking means at each of the image planes for masking off complementary halvesof the image and relay lens means for relaying the unmasked parts of both images to each eyepiece.

STEPHEN M. MAcNElLLE. 

